The demand for increased storage capacity in memory or rigid disks and the trend towards miniaturization of memory or rigid disks (e.g., due to the requirement for smaller hard drives in computer equipment) continues to emphasize the importance of the memory or rigid disk manufacturing process, including the planarization or polishing of such disks for ensuring maximal performance. While there exist several chemical-mechanical polishing (CMP) compositions and methods for use in conjunction with semiconductor device manufacture, few conventional CMP methods or commercially available CMP compositions are well-suited for the planarization or polishing of memory or rigid disks.
As the demand for greater storage capacity has increased, so has the need for improved processes for the polishing of such memory or rigid disks. The term “memory or rigid disk” refers to any magnetic disk, hard disk, rigid disk, or memory disk for retaining information in electromagnetic form. The memory or rigid disk typically has a surface that comprises nickel-phosphorus, but the memory or rigid disk surface can comprise any other suitable material. The planarity of the memory or rigid disks must be improved, as the distance between the recording head of a disk drive and the surface of the memory or rigid disk has decreased with improvements in recording density that demand a lower flying height of the magnetic head with respect to the memory or rigid disk. In order to permit a lower flying height of the magnetic head, improvements to the surface finish of the memory or rigid disk are required.
Surface characteristics of memory or rigid disks affecting the flying height of the magnetic head include waviness and microwaviness. Waviness or warp is a gross deviation from flatness over the entire disk surface. Waviness is generally due to the fact that the disk is readily susceptible to warping as a result of its very thin, annular shape, and to various internal stresses introduced during formation of the disk. An intermediate form of surface deviation, herein referred to as microwaviness, may exist. As used herein, microwaviness is a waviness of a disk surface for a range of wavelengths that are on the order of the length of the transducing head. Using current head technology, these wavelengths are approximately in the range of 10 to 5000 microns. For low flying head heights, microwaviness can create an airbearing resonance, thereby causing excessive head to disk spacing modulation. The spacing modulation resulting from microwaviness can cause poor overwriting of data on the disk surface, and in some cases can even cause collision of the head with the disk surface with resulting damage to the disk surface and/or the recording head.
During the polishing of a memory or rigid disk, typically the edges of the disk receive a higher pressure from the polishing tool than the remaining surface area of the disk. Typically, polishing is performed using a combination of an abrasive, a polishing pad, and a liquid carrier, in which the abrasive may be suspended in the liquid carrier, or may be affixed to the surface of the pad. As the polishing process mainly consists of mechanical abrasion of the disk by the abrasive and/or pad, in conjunction with the action of chemicals that may be present, and the rate of abrasion is at least in part a function of pressure applied, the edges of the disk experience a higher rate of abrasion than the rest of the disk. This leads to the formation of a curved, or rounded, contour at the edges of the disk, known in the art as edge roll-off, rub-off, or dub-off. Such rounded areas on a disk are unsuitable for recording. Thus, if the amount of roll-off can be reduced, the recording capacity for a disk can be increased.
As the polishing rate (i.e., removal rate) of the memory or rigid disk is increased, edge roll-off typically decreases, however the microwaviness of the disk typically increases. Thus, there remains a need in the art for polishing compositions and methods for planarizing or polishing memory or rigid disks which minimize microwaviness and edge roll-off, without sacrificing the removal rate of the memory or rigid disk.